Encryption of compressed multimedia content is an increasingly common requirement by the content industry and is a requirement to comply with various robustness rules in Digital Rights Management (DRM) standards. A general rule of thumb is that in order to effectively prevent an unauthorized copying of media contents such as for instance a High Definition (HD) video, the media content must not be stored in memories in an electronic device without also being encrypted.
One problem for current encryption schemes is that known rendering engines do not access memories in a linear pattern. Rather, the frame store represents a two-dimensional (2D) picture, and a rendered object may move freely within this frame. Known decryption methods based on block ciphers and stream ciphers do not easily handle accesses of this type or arbitrary size and position in a larger 2D block of encrypted content. In the case of HD graphics for example, the frame store is of the order 1920×1080×32 bits. It is apparent that it is impractical to decrypt a frame store of this size in order just for obtaining a much smaller data content section for processing.
An additional problem to make memory encryption hard is that one must not add a significant latency to memory read operations. Any complex operations during encryption may upset the timing of the platform and render the encryption scheme useless for a user.
WO 03/048939 discloses a method for cryptographically protecting secure content in connection with a graphics subsystem of a computing device. Techniques are implemented to encrypt the contents of video memory so that unauthorized software cannot gain meaningful access to it, thereby maintaining confidentiality. Moreover, a mechanism for tamper detection is provided so that there is awareness when data has been altered in some fashion, thereby maintaining integrity. In various embodiments, the contents of overlay surfaces and/or command buffers are encrypted, and/or a graphic processing unit is able to operate on encrypted content while preventing its availability to untrusted parties, devices or software.
US 2003/0135742 discloses a method and a system for protecting data that is intended for use and processed on video or graphics cards. In various embodiments, data that is intended for use by a video card can be encrypted such that any time the data is provided onto a bus between the video card and the computer system. For example, when data is moved from memory on the video card to the system's memory and vice versa, the data is in encrypted form and thus protected.
U.S. Pat. No. 6,711,683 discloses a computing system that prevents unauthorized use of compressed video data stored in a first-in-first-out memory buffer of a set top box. A single integrated circuit includes a data processor and a chip identity read only register storing a unique chip identity number fixed during manufacture. The data processor encrypts the compressed video data stream using the chip identity number as an encryption key. This encrypted data is stored in and recalled from a First In-First Out (FIFO) buffer. The data processor then decrypts the recalled data employing at least a part of the chip identity number as the decryption key. Using this technique the compressed video data stream temporarily stored in compressed form in the FIFO buffer can only be employed by the particular data processor having the unique chip identity number.
There may be a need for providing an advanced encryption and decryption scheme, which is in particular effective for data contents comprising a two dimensional structure.